Why is decay important for plant growth

Without nitrogen fertilizers, scientists estimate that we would lose up to one third of the crops we rely on for food and other types of agriculture.

But we need to know how much nitrogen is necessary for plant growth, because too much can pollute waterways, hurting aquatic life. Nitrogen is a key element in the nucleic acids DNA and RNA , which are the most important of all biological molecules and crucial for all living things. DNA carries the genetic information, which means the instructions for how to make up a life form. When plants do not get enough nitrogen, they are unable to produce amino acids substances that contain nitrogen and hydrogen and make up many of living cells, muscles and tissue.

Without amino acids, plants cannot make the special proteins that the plant cells need to grow. Without enough nitrogen, plant growth is affected negatively. With too much nitrogen, plants produce excess biomass, or organic matter, such as stalks and leaves, but not enough root structure. In extreme cases, plants with very high levels of nitrogen absorbed from soils can poison farm animals that eat them [ 3 ].

Excess nitrogen can also leach—or drain—from the soil into underground water sources, or it can enter aquatic systems as above ground runoff. This excess nitrogen can build up, leading to a process called eutrophication. Eutrophication happens when too much nitrogen enriches the water, causing excessive growth of plants and algae.

When the phytoplankton dies, microbes in the water decompose them. Organisms in the dead zone die from lack of oxygen.

These dead zones can happen in freshwater lakes and also in coastal environments where rivers full of nutrients from agricultural runoff fertilizer overflow flow into oceans [ 4 ]. Can eutrophication be prevented? People who manage water resources can use different strategies to reduce the harmful effects of algal blooms and eutrophication of water surfaces. They can re-reroute excess nutrients away from lakes and vulnerable costal zones, use herbicides chemicals used to kill unwanted plant growth or algaecides chemicals used to kill algae to stop the algal blooms, and reduce the quantities or combinations of nutrients used in agricultural fertilizers, among other techniques [ 5 ].

But, it can often be hard to find the origin of the excess nitrogen and other nutrients. Once a lake has undergone eutrophication, it is even harder to do damage control. Algaecides can be expensive, and they also do not correct the source of the problem: the excess nitrogen or other nutrients that caused the algae bloom in the first place!

Another potential solution is called bioremediation , which is the process of purposefully changing the food web in an aquatic ecosystem to reduce or control the amount of phytoplankton. For example, water managers can introduce organisms that eat phytoplankton, and these organisms can help reduce the amounts of phytoplankton, by eating them! The nitrogen cycle is a repeating cycle of processes during which nitrogen moves through both living and non-living things: the atmosphere, soil, water, plants, animals and bacteria.

In order to move through the different parts of the cycle, nitrogen must change forms. In the atmosphere, nitrogen exists as a gas N 2 , but in the soils it exists as nitrogen oxide, NO, and nitrogen dioxide, NO 2 , and when used as a fertilizer, can be found in other forms, such as ammonia, NH 3 , which can be processed even further into a different fertilizer, ammonium nitrate, or NH 4 NO 3.

There are five stages in the nitrogen cycle, and we will now discuss each of them in turn: fixation or volatilization, mineralization, nitrification, immobilization, and denitrification.

In this image, microbes in the soil turn nitrogen gas N 2 into what is called volatile ammonia NH 3 , so the fixation process is called volatilization. Leaching is where certain forms of nitrogen such as nitrate, or NO 3 becomes dissolved in water and leaks out of the soil, potentially polluting waterways.

In this stage, nitrogen moves from the atmosphere into the soil. To be used by plants, the N 2 must be transformed through a process called nitrogen fixation. Fixation converts nitrogen in the atmosphere into forms that plants can absorb through their root systems. A small amount of nitrogen can be fixed when lightning provides the energy needed for N 2 to react with oxygen, producing nitrogen oxide, NO, and nitrogen dioxide, NO 2.

These forms of nitrogen then enter soils through rain or snow. Nitrogen can also be fixed through the industrial process that creates fertilizer. This form of fixing occurs under high heat and pressure, during which atmospheric nitrogen and hydrogen are combined to form ammonia NH 3 , which may then be processed further, to produce ammonium nitrate NH 4 NO 3 , a form of nitrogen that can be added to soils and used by plants.

The world would be very different if the rates at which things decay were to change. To find out how different, Nadelhoffer and other scientists are probing rot in forests around the world. They call one series of these experiments DIRT.

It stands for Detritus Input and Removal Treatments. Detritus is debris. In a forest, it includes the leaves that fall and litter the ground. Scientists on the DIRT team add or remove leaf litter from particular parts of a forest.

The researchers then measure what happens to each plot. Over time, leaf-starved forest soils undergo a range of changes. Scientists refer to the carbon-rich materials released from once-living organisms as organic matter.

Soils deprived of leaf litter have less organic matter. The soils deprived of leaf litter also do a poorer job of releasing nutrients back to plants. The types of microbes present and the numbers of each also change.

Meanwhile, forest soils given bonus leaf litter become more fertile. Some farmers use the same idea. Tilling means plowing. That can reduce soil erosion and runoff. Less runoff means soils will lose fewer nutrients. A much larger experiment is going on worldwide. Scientists refer to it as climate change. Much of that increase comes from people burning oil, coal and other fossil fuels. That burning adds carbon dioxide and other gases to the air.

It comes down to something called feedbacks. Feedbacks are outside changes to a process, such as global warming. Feedbacks can either increase or decrease the pace at which some change occurs. For example, higher temperatures can lead to more decomposition. And if climate change speeds rot, it will also speed how quickly more carbon dioxide enters the atmosphere.

She is a biologist at the University of New Hampshire in Durham. And now a feedback cycle develops. In fact, the situation is more complicated, Mayes cautions.

To learn more, Mayes, Gangsheng Wang and other soil researchers at Oak Ridge National Laboratory created a computer program to model how global warming and other aspects of climate change would affect the speed at which dead things break down.

This analysis accounted for those times of the year when microbes are dormant, or inactive. It appears that after a few years, microbes may simply adjust to higher temperatures, Mayes explains. Simply put: Predicting future consequences is difficult. Outdoor experiments provide more insights. For more than two decades now, experts there have used underground electric coils to artificially warm certain soil plots. More carbon going into the air means less remains in the topsoil.

A wide range of organisms takes part in the decomposition process. Most of them are inconspicuous and unglamorous. From a conventional human perspective, they are even undesirable. The detritivore community includes insects such as beetles and their larvae as well as flies and maggots fly larvae.

It also includes woodlice, fungi , slime moulds, bacteria, slugs and snails, millipedes, springtails and earthworms. Almost all of them are tiny, and their function happens gradually in most cases, over months or years. But together they convert dead plants and animals into forms that are useable either by themselves or other organisms. The primary decomposers of most dead plant material are fungi. Dead leaves fall from trees and herbaceous plants collapse to the ground after they have produced seeds.

These form a layer of litter on the soil surface. The litter layer can be quite substantial in volume. The litter fall in a Scots pine is around The litter is quickly invaded by the hyphae of fungi. Hyphae are the white thread-like filaments that are the main body of a fungus.

The mushrooms that appear on the forest floor, are merely the fruiting bodies of the fungus. The hyphae draw nourishment from the litter. This enables the fungi to grow and spread, while breaking down the structure of the dead plant material. Bacteria also play a part in this process, as do various invertebrates, including slugs, snails and springtails. As the decay becomes more advanced, earthworms begin their work.

This decomposition process is usually odourless. It is aerobic, meaning that it takes place in the presence of air oxygen in particular. On the forest floor it is spread out in both space and time. When people make compost heaps in their garden, they are utilising the same process.

It is concentrated and accelerated by piling the dead material together in a heap, and the heat that is generated speeds up the process of decay. Fungi that feed on dead plant material are called saprotrophic fungi. Common examples include the horsehair parachute fungus, which can be seen growing out of dead grass stems, leaves or pine needles.

Another is the sulphur tuft fungus, which fruits on logs that are at an advanced state of decomposition. In a forest, the rate of decomposition depends on what the dead plant material is. Leaves of deciduous trees and the stems and foliage of non-woody plants generally break down quickly.

They are usually gone within a year of falling to the forest floor. Some plant material, such as the fibrous dead fronds of bracken , takes longer. But even these will still be decomposed within three years. The needles of conifers, such as Scots pine, are much tougher.

It can take up to seven years for them to be completely broken down and recycled. The rate of decay is also determined by how wet the material is, and in general the wetter it is the faster it breaks down. In dry periods or dry climates, the organic matter becomes dessicated. Many detritivores, such as fungi and slugs, are inactive so the decomposition process becomes prolonged. In contrast to the softer tissues of herbaceous plants, the fibres of trees and other woody plants are much tougher and take a longer time to break down.

Fungi are still, for the most part, the first agents of decay, and there are many species that grow in dead wood. The common names of species such as the wet rot fungus and the jelly rot fungus indicate their role in helping wood to decompose. The growth of the fungal hyphae within the wood helps other detritivores, such as bacteria and beetle larvae, to gain access. The fungi feed on the cellulose and lignin, converting those into their softer tissues. These in turn begin to decompose when the fungal fruiting bodies die.

Many species of slime mould also grow inside dead logs and play a role in decomposition. Like fungi, they are generally only visible when they are ready to reproduce and their fruiting bodies appear. Some decomposers are highly-specialised. For example, the earpick fungus grows out of decaying Scots pine cones that are partially or wholly buried in the soil.

Another fungus known as Cyclaneusma minus grows on the fallen needles of Scots pine. As the wood becomes more penetrated and open, through, for example, the galleries produced by beetle larvae, it becomes wetter.